The effect of varying albumin concentration and hydrostatic pressure on hydraulic conductivity and albumin permeability of cultured endothelial monolayers.

An in vitro model of the endothelial transport barrier was developed using bovine aortic endothelial cell monolayers cultured on a porous polycarbonate substrate. Hydraulic conductivity (Lp) was measured by a bubble tracking technique at varying pressure differentials and albumin concentrations. The effective albumin permeability (Pc) was determined by measuring the flux of fluorescent-labeled albumin across monolayers at varying hydrostatic pressures. Lp determined at pressure differentials between 5.0 and 10 cm H2O demonstrated a strong dependence on albumin concentration, decreasing approximately 10-fold from 21.3 x 10(-7) +/- 3.18 x 10(-7) cm/sec/cm H2O (mean +/- SEM) at 0.0 g/dl to 2.35 x 10(-7) +/- 0.20 x 10(-7) cm/sec/cm H2O at 1.0 g/dl albumin. Increasing the albumin concentration from 1.0 to 4.0 g/dl reduced Lp by an additional 16% to 1.97 x 10(-7) +/- 0.17 x 10(-7) cm/sec/cm H2O. Furthermore, Lp was moderately dependent on the pressure differential, increasing by about a factor of two with a doubling of the pressure differential. The effective permeability (Pc) was also dependent on the pressure differential. At an albumin concentration of 4.0 g/dl, Pc increased from 1.37 x 10(-6) +/- 0.26 x 10(-6) cm/sec at 0.0 cm H2O to 5.06 x 10(-6) +/- 1.92 x 10(-6) cm/sec at 10 cm H2O. Analysis of Pc and Jv data, however, demonstrates that water and albumin do not share a common pathway in crossing the endothelial monolayer. These data suggest the existence of a large pore pathway for albumin. Thus, the in vitro system has many of the transport characteristics of intact vessels in vivo and should be useful for physiological studies of the endothelial transport barrier.